It is critical to understand that greenhouse gases do not trap incoming short-wave radiation, but rather the long-wave radiation released by the Earth's surface as a result of absorbing short-wave radiation. Figure 5 depicts the Earth's radiation budget. Greenhouse gases block some of the outgoing long-wave radiation, which would otherwise escape into space. But they don't affect the amount of incoming short-wave radiation from the sun.
Some of the longer wave energy radiates back into the atmosphere and into space as the short wave energy heats the surface. Some of the energy is absorbed by greenhouse gases and trapped in the lower atmosphere. The Earth is warmer because less heat radiates into space. This means that more of the absorbed light will eventually reach the surface than if there were no greenhouse effect.
The main greenhouse gas on Earth is carbon dioxide, which accounts for about 85% of the total greenhouse effect. Other significant factors include methane and nitrous oxide. Changes in the amount these gases in the atmosphere affect how much heat gets locked up in the ground or ocean bed.
Greenhouse gases can be released into the atmosphere through natural processes or by human activity. For example, volcanoes emit large amounts of carbon dioxide into the atmosphere, while people burn fossil fuels like oil and coal, which contain carbon, to power vehicles and heat buildings. The amount of carbon dioxide in the atmosphere has increased since the beginning of the industrial revolution, when humans started burning fossil fuels instead part solar energy.
Climate change is defined as a long-term increase in the average temperature of the Earth's surface and its oceans, which may be caused by increased absorption of radiation into the atmosphere from the sun. Climate change affects all parts of the world, but it takes place over many decades or centuries - not minutes or hours.
Greenhouse Gas Emissions Greenhouse gases (such as water vapor and carbon dioxide) in the atmosphere absorb the majority of the Earth's radiated longwave infrared radiation, which warms the lower atmosphere. As a result, there is strong evidence that increases in atmospheric CO2 concentration have been responsible for most of the increase in global average temperature since the mid-20th century.
Greenhouse gases (such as water vapor and carbon dioxide) in the atmosphere absorb the majority of the Earth's radiated longwave infrared radiation, which warms the lower atmosphere. Other gases such as ozone and clouds also play a role.
Terrestrial radiation is energy transferred to or from the earth's surface and its atmosphere. It can be divided into two components: shortwave radiation, which results from the heat of the sun entering the earth's atmosphere and being reflected back towards it; and longwave radiation, which is emitted by the earth itself and enters the atmosphere. Longwave radiation comprises infrared radiation and radio waves, with the former dominating at mid-to-high latitudes and the latter at the poles. Infrared radiation is absorbed by atmospheric gases such as oxygen and nitrogen as well as liquid water, while radio waves are not absorbed by gases but instead are transmitted through them.
The greenhouse effect occurs when increased levels of greenhouse gases in the atmosphere lead to further absorption of infrared radiation, thereby causing the average temperature of the planet to rise. As a result, more infrared radiation is absorbed which leads to further increases in temperature. This positive feedback mechanism can lead to significant global warming.
The atmosphere also acts as a barrier to solar radiation.
When this long-wavelength radiation collides with greenhouse gas molecules in the atmosphere, the molecules absorb it, warming the atmosphere until the emitted energy matches the absorbed energy. This effect is called "radiation trapping."
Greenhouses use this same principle to heat their enclosed spaces. The glass walls of the greenhouse block most of the short-wave light (that is, light with wavelengths less than about 550 nanometers), but they let through some of the longer-wavelength light (those with wavelengths greater than about 550 nm). This remaining light can enter the building and be reflected back toward the source by its interior surfaces, causing it to heat up too.
The key word here is "trap". Longer-wavelength light that enters a greenhouse will always travel farther than shorter-wavelength light, so it makes sense for a greenhouse to only allow through as much longer-wavelength light as it needs to maintain an equal amount of heat within the building. Any more would just be wasted energy.
That's why greenhouses tend to be hot houses. The more glass they have, the more long-wave radiation is trapped and the hotter they get. A very transparent greenhouse will cause parts of it to become completely dark at certain times of the day due to all the short-wave light being blocked out.